Various methods and devices are known in the art for providing a spray of heated water or other washing fluid onto the windows of a vehicle. The heated fluid is particularly advantageous in removing ice from the vehicle windshield in cold weather. This ice removal function requires that a driver of the vehicle wait while the fluid is heated, before the windshield can be de-iced. Methods and devices known in the art are impractical for this purpose, however, since they typically use heat or electricity generated by the vehicle engine itself to heat the fluid, requiring the driver to wait an unacceptably long time for the fluid to reach a suitable temperature.
Using the vehicle battery to heat the fluid, independent of the vehicle engine, is also problematic because of the large current draw required to heat a sufficient quantity of fluid to effectively de-ice the windshield. The battery cannot typically provide sufficient current to heat the vehicle's entire reservoir of washing fluid in a reasonable amount of time. Although methods and devices have been suggested for heating the fluid on-line, as it is about to be sprayed on the windshield, the battery also cannot provide enough current to heat a spray of sufficient volume to a high enough temperature to achieve effective de-icing.
U.S. Pat. No. 5,509,606 describes a hot wash device for an automobile windshield, which includes a container into which washing fluid from a reservoir is pumped and in which the fluid is heated by an electrical heating element before it is sprayed onto the windshield. The container is insulated and includes a thermostat that is used to ensure that the temperature of the fluid does not exceed a predetermined maximum. The container is kept full, with heat applied as needed to bring the cold fluid pumped into the container up to the desired temperature.
U.S. Pat. No. 5,118,040 describes electric apparatus for washing window glass of a vehicle. An insulated container is positioned between a reservoir of cold washing fluid and spray outlets to the vehicle window, in a position lower than the reservoir so as to be kept full of fluid. When the vehicle ignition is turned on, an electric heater heats the fluid in the container and remains active while the vehicle is in use. There is no provision, however, for rapid start-up and heating to de-ice the vehicle window.
U.S. Pat. No. 4,090,668 describes a windshield washing and deicing system which includes a reservoir having a sealed container therein. A pump transfers washer fluid from the reservoir to the container and from the container to a plurality of nozzles. Heated engine coolant is passed through a conduit in the reservoir. Electrical resistance wire heats the fluid in the container whenever the temperature drops below a certain minimum. Solenoid valves direct the spray from the tank to the front or rear window of the vehicle, but there is no suggestion of using the valves for any other fluid control purposes.
U.S. Pat. No. 5,012,977 describes a vehicle window washer in which washer fluid in a reservoir is heated, and in which a pump for spraying the fluid on the vehicle window has a variable outlet pressure. The temperature of the fluid in the reservoir is sensed, and the pump outlet pressure is varied accordingly in an inverse manner with temperature of the washer fluid, so as to maintain a more consistent fluid deposit on the window, as the fluid viscosity changes with temperature.
U.S. Pat. No. 5,354,965 describes a system for electrically heating a volume of windshield cleaning fluid in a motor vehicle. A vessel is filled with the volume of fluid to be heated, using PTC thermistors or other electrical heating elements. A control circuit regulates the length of time that the fluid is heated, in accordance with a prevailing ambient temperature, before the fluid is sprayed on the windshield. The circuit also prevents operation of the fluid heating when the vehicle engine is not running.
PCT Application PCT/US98/13023, assigned to the present assignee, describes de-icing apparatus in which a vessel is provided for heating a washing fluid before the fluid is discharged toward a window of a vehicle. Before the fluid is introduced into the vessel, the vessel is preheated, preferably by passing an electrical current through a heating element in the vessel for about one minute or less. When preheating is completed, the fluid is allowed into the vessel and is rapidly heated by contact therewith, leading to an increase in pressure in the vessel due to vaporization of a portion of the fluid. The fluid is then discharged at a desired temperature and pressure so as to clean and/or de-ice the window.
Although the preheating of the vessel draws only a moderate electrical input from the vehicle battery, it enables a sufficient quantity of hot fluid to be generated for de-icing the window before starting the vehicle more rapidly than in any practical window cleaning system known in the art. Moreover, the pressure generated by vaporization of the fluid helps to clear ice or other blockages that may have formed in tubing or nozzles through which the fluid is sprayed onto the window. It is also noted that spraying the heated fluid on the window's exterior surface effectively defogs its interior surface, as well.